Bosentan is an endothelin receptor antagonist, belonging to a class of highly substituted pyrimidine derivatives. Bosentan is marketed in its monohydrate form chemically known as 4-tert-butyl-N-[6-(2-hydroxy-ethoxy)-5-(2-methoxy-phenoxy)-[2,2′]-bipyrimidin-4-yl]-benzene sulfonamide monohydrate, which is represented by Formula 1.

Bosentan is useful for the treatment of pulmonary arterial hypertension (PAH) to improve exercise capacity and symptoms in patients with Grade III functional status.
U.S. Pat. No. 5,292,740 describes a purification method for bosentan with column chromatography using toluene and ethyl acetate mixture, and U.S. Pat. No. 6,136,971 describes a purification method for bosentan involving drop-wise addition of water to the refluxing ethanolic solution of bosentan. However, these patents do not refer to any polymorphic form of bosentan.
WO 2008/135795 describes Form 1, Form 2, Form 3, Form 4 and an amorphous form of bosentan characterized by their XRPD, IR and DSC patterns. WO 2009/047637 describes Form A1, Form A2, Form A4 and an amorphous form of bosentan characterized by their XRPD, IR and DSC patterns and the processes for their preparation. WO 2009/093127 describes crystalline Form A5 of bosentan.
WO 2009/083739 describes anhydrous crystalline Forms B and C of bosentan and Form A of amorphous bosentan characterized by their XRPD, IR and DSC patterns. It also describes calcium and barium salts of bosentan along with the processes for their preparation.